Liquid-feed Flame Spray Pyrolysis Research Articles

Nanocomposite Li- and Mn-rich spinel cathodes characterized with a green, aqueous binder system

There is a growing need for alternatives to commercialized high-energy–density cathodes for Li-ion batteries with chemistries less dependent on Co and Ni and, in the past decade, particular attention has been placed on Li- and Mn- rich cathodes. Herein we report synthesis and characterization of Li- and Mn-rich cathode active materials (CAMs) with spinel-based nanocomposite structure having stoichiometries LixMn1.5Ni0.5O4 (x = 0.45–1.50) synthesized via liquid-feed flame spray pyrolysis. When cycled from 4.9 to 2.4 V, LixMn1.5Ni0.5O4 (x = 1.26, 1.50) exhibited energy densities greater than 1000 Wh kgCAM-1 using a green, aqueous binder system. Increasing initial Li content results in larger 1st charge capacity, which can potentially serve as a Li donor to irreversible, Li-consuming solid electrolyte interphase formation in next generation anode active materials.

Liquid-feed flame spray pyrolysis enabled synthesis of Co- and Cr-free, high-entropy spinel oxides as Li-ion anodes

Liquid-feed flame spray pyrolysis enabled synthesis of Co- and Cr-free, high-entropy spinel oxides as Li-ion anodes

One-Step Synthesis of Versatile Antimicrobial Nano-Architected Implant Coatings for Hard and Soft Tissue Healing.

Dental implant failure remains a prevalent problem around the globe. The integration of implants at the interface of soft and hard tissues is complex and susceptible to instability and infections. Modifications to the surface of titanium implants have been developed to improve the performance, yet insufficient integration and biofilm formation remain major problems. Introducing nanostructures on the surface to augment the implant-tissue contact holds promise for facilitated implant integration; however, current coating processes are limited in their versatility or costs. We present a highly modular single-step approach to produce multicomponent porous bioactive nanostructured coatings on implants. Inorganic nanoparticle building blocks with complex compositions and architectures are synthesized in situ and deposited on the implants in a single step using scalable liquid-feed flame spray pyrolysis. We present hybrid coatings based on ceria and bioglass, which render the implant surfaces superhydrophilic, promote cell adhesion, and exhibit antimicrobial properties. By modifications to the bioglass/ceria nanohybrid composition and architecture that prevent biomineralization, the coating can instead be tailored toward soft tissue healing. The one-step synthesis of nano-architected tissue-specific coatings has great potential in dental implantology and beyond.

Improved Electrochemical Properties of Li4Ti5O12 Nanopowders (NPs) via Addition of LiAlO2 and Li6SiON Polymer Electrolytes, Derived from Agricultural Waste

Li4Ti5O12 (LTO) has received considerable interest as an alternate anode material for high power density batteries for large scale applications. However, LTO suffers from poor Li+ diffusivity and poor electronic conductivity, resulting in capacity loss and poor rate performance. Here we demonstrate a facile synthesis of LTO NPs using liquid-feed flame spray pyrolysis (LF-FSP) which provides high surface area (∼38 m2/g) spinel structure LTO NPs with average particle sizes (APSs) of 45 ± 0.3 nm. Pristine LTO-Li half-cells exhibit reversible capacity of 70 mAh/g at 10 C. In this study, we show that mixing LiAlO2 NPs (5 wt %) and Li6SiON polymer precursor (10 wt %) with pristine LTO via ball-milling and ultrasonication followed by tape casting enhances the LTO rate performance providing reversible capacity of ∼217 mAh/g at 5 C over 500 cycles. The Li6SiON polymer electrolyte is synthesized from rice hull ash (RHA), an agricultural waste, providing a green synthetic approach to electrode coating materials. CV and EIS studies indicate that adding the solid and polymer electrolytes reduces charge-transfer resistance and electrode polarization, enhancing both reversibility and the LTO Li+ diffusion coefficient from 4.6 × 10–14 to 2.7 × 10–12 cm2/s.

Solid Electrolytes Derived From Precursors and Liquid-Feed Flame Spray Pyrolysis Nano-Powders to Enable the Assembly of All-Solid-State-Batteries

Solid Electrolytes Derived From Precursors and Liquid-Feed Flame Spray Pyrolysis Nano-Powders to Enable the Assembly of All-Solid-State-Batteries

LiAlO2/LiAl5O8 Membranes Derived from Flame-Synthesized Nanopowders as a Potential Electrolyte and Coating Material for All-Solid-State Batteries.

Recently, γ-LiAlO2 has attracted considerable attention as a coating in Li-ion battery electrodes. However, its potential as a Li+ ceramic electrolyte is limited due to its poor ionic conductivity (<10-10 S cm-1). Here, we demonstrate an effective method of processing LiAlO2 membranes (<50 μm) using nanopowders (NPs) produced via liquid-feed flame spray pyrolysis (LF-FSP). Membranes consisting of selected mixtures of lithium aluminate polymorphs and Li contents were processed by conventional tape casting of NPs followed by thermocompression of the green films (100 °C/10 kpsi/10 min). The sintered green films (1100 °C/2 h/air) present a mixture of LiAlO2 (∼72 wt %) and LiAl5O8 (∼27 wt %) phases, offering ionic conductivities (>10-6 S cm-1) at ambient with an activation energy of 0.5 eV. This greatly increases their potential utility as ceramic electrolytes for all-solid-state batteries, which could simplify battery designs, significantly reduce costs, and increase their safety. Furthermore, a solid-state Li/Li3.1AlO2/Li symmetric cell was assembled and galvanostatically cycled at 0.375 mA cm-2 current density, exhibiting a transference number ≈ 1.

Processing combustion synthesized Mg0.5Zr2(PO4)3 nanopowders to thin films as potential solid electrolytes

Mg0.5Zr2(PO4)3 is a promising electrolyte for Mg solid-state batteries. But it is difficult to achieve high-density thin films with phase purity. Here, we synthesized Mg0.5(1+x)FexZr2−x(PO4)3 nanopowders using liquid-feed flame spray pyrolysis and used the product to form transparent thin films via simple pressureless sintering at 1100 °C. The influence of Fe on the phase and microstructure were discussed and the bottlenecks during Mg2+ conduction pathway were calculated. The dense and high-purity Mg0.6Fe0.2Zr1.8(PO4)3 exhibited an extremely low ionic area specific resistance of 1.6 kΩ cm2 at 200 °C. This paper presents a method for preparing dense, high-purity solid electrolytes at modest sintering temperatures.

Photocatalytic La4Ti3O12 nanoparticles fabricated by liquid-feed flame spray pyrolysis

Hexagonal plate-like nanoparticles (NPs) of the layered perovskite La4Ti3O12 were fabricated using liquid-feed flame spray pyrolysis (LF-FSP) followed by subsequent heat-treatments. Their photocatalytic activity was evaluated using decolorization of methyl orange solutions under Uv irradiation. LF-FSP combusts metalloorganic precursor aerosols to produce mixtures of cubic simple perovskite (ABO3) phase and lanthanum oxycarbonate (La2O4·846C0.846) phase with very low agglomeration and average particle sizes (APSs) of 23 nm (as-produced NPs). Rietveld refinement of synchrotron XRD powder patterns verified that the simple perovskite in the as-produced NPs is LaTiO3 (originally cubic Pm-3m-type space group) and heat-treating gives NPs of the trigonal layered perovskite La4Ti3O12 (R-3-type space group). La4Ti3O12 NPs heat-treated at 1100 °C/3-6h/air exhibits hexagonal plate-like morphology and high crystallinity offering enhanced photocatalytic degradation of methyl orange solutions compared to the as-produced NPs. The LF-FSP approach to obtaining layered perovskite La4Ti3O12 NPs provides a simple route to photocatalytic materials in reasonable quantities.

Fe Doped, Dense, High Phase Purity and Nano-Grained Mg0.5zr2(Po4)3 Thin Films

Mg0.5Zr2(PO4)3 is a priority electrolyte for Mg solid state batteries. However, it is difficult to achieve high density and phase purity simultaneously, especially in thin films. Here, we processed liquid-feed flame spray pyrolysis synthesized MZPFex nanopowders to make transparent films via simple pressureless sintering at 1100°C. The influence of Fe on the phase and microstructure are discussed. In particular, dense and high phase purity Mg0.6Fe0.2Zr1.8(PO4)3 exhibits extremely low ionic area specific resistance, 1.6 kΩ cm2. This paper presents an effective method to prepare dense, high phase purity solid electrolytes at modest sintering temperatures.

Preparation of Nb-doped TiO2 nanopowder by liquid-feed spray pyrolysis followed by ammonia annealing for tunable visible-light absorption and inhibition of photocatalytic activity

Visible-light absorbing TiO2 with color tunability and negligible photocatalytic activity was developed by synthesizing Nb-doped TiO2 using liquid-feed flame spray pyrolysis (LF-FSP) followed by NH3 annealing. Nb-doped TiO2 nanopowders with selected Nb contents were synthesized by changing ratios of metalloorganic precursors. By using Ti and Nb precursors whose thermal decomposition behavior is very similar, the maximum Nb doping concentration was improved compared to Nb-doped TiO2 prepared by flame spray pyrolysis (FSP) in previous reports. As-synthesized Nb-doped TiO2 nanopowders were white regardless of the Nb content, while all became colored after NH3 annealing. In addition, the color of Nb-doped TiO2 after NH3 annealing varied from yellow to dark green depending on the Nb content. Light absorption characterization indicates that the color variation is attributable to the localized levels formed by interstitial N-doping and Nb-doping-induced Ti3+ formation resulting from reduction by H2, formed as a result of NH3 decomposition.

Chemical modification in and on single phase [NiO]0.5[Al2O3]0.5 nanopowders produces “chocolate chip‐like” Nix@[NiO]0.5‐x[Al2O3]0.5 nanocomposite nanopowders

AbstractPhase‐pure [NiO]0.5[Al2O3]0.5 spinel nanoparticles (NPs) with limited aggregation were obtained via liquid‐feed flame spray pyrolysis (LF‐FSP) by combusting metalloorganic precursor solutions. Thereafter “chocolate chip‐like” Nix[NiO0.5‐x][Al2O3]0.5 nanoparticles consisting of primary [NiO0.5‐x][Al2O3]0.5 particles with average particle sizes of 40‐60 nm decorated with Ni metal particles (&lt;10 nm in diameter) dispersed on the surface were synthesized by heat treating the spinel NPs at 800°C/7 h in flowing 5% H2:N2 100 mL/min in a fluidized bed reactor. The synthesized materials were characterized using TEM, XRD, FTIR, and TGA/DTA. The Ni depleted areas consist primarily of γ‐Al2O3. The Ni content (800°C) was determined by TGA to be ≈11.3 wt.% based on TGA oxidation behavior. The successful synthesis of such nanocomposites with limited aggregation on a high temperature support provides a facile route to synthesize well‐defined NP catalysts. This work serves as a baseline study for an accompanying paper, wherein thin, flexible, dense films made from these same NPs are used as regenerable catalysts for carbon nanotube syntheses.

Engineering the Bioactivity of Flame-Made Ceria and Ceria/Bioglass Hybrid Nanoparticles.

Despite its use as a highly efficient and reusable catalyst in research and industrial settings, cerium oxide nanoparticles or nanoceria have yet to gain a foothold in the biomedical field. A variety of beneficial effects of nanoceria have been demonstrated, including its use as an inorganic nanoenzyme to mimic antioxidant enzymes, to protect mammalian cells, and to suppress microbial growth. While these properties are of high interest for wound-management applications, the literature offers contradicting reports on toxicity and enzymatic activity of nanoceria. These discrepancies can be attributed to differences between synthesis methods and insufficient physicochemical characterization, leading to incomparable studies. The activity of nanoceria is mostly governed by its Ce3+/Ce4+ ratio which needs to be controlled to compare different nanoceria systems. In this work, we demonstrate that liquid-feed flame spray pyrolysis offers excellent control over the oxidation state in a one-step synthesis of nanoceria. This control allows a comprehensive comparison of different types of ceria nanoparticles. We connect physicochemical characteristics to biomedically relevant properties such as superoxide dismutase and catalase mimicry, human monocyte and macrophage protection, and antimicrobial activity. Furthermore, we demonstrate how the synthesis method also allows tailoring the properties of ceria/bioglass hybrid nanoparticles, thus creating nanoparticles with manifold biomedical prospects.

Liquid-feed flame spray pyrolysis derived nanopowders (NPs) as a route to electrically conducting calcium aluminate (12CaO.7Al2O3) films

Traditionally, C12A7 materials have been processed via solid-state reaction followed by pulsed laser deposition (PLD) or floating zone (Fz) crystallization methods at high temperature, high cost approaches to single-phase films. These techniques require a significant number of process steps to generate C12A7:e− materials that have been shown to exhibit exceptional electrical conductivities as high as 1 S/cm. We demonstrate here an effective alternative method using flame made C12A7 nanopowders (NPs) produced via liquid-feed flame spray pyrolysis (LF-FSP). Nearly fully dense, single phase, and transparent C12A7 films (< 50 μm) can be produced by processing these NPs into green films by tape-casting, thermo-compression and then sintering to 1300 ℃/3 h/O2. Subsequent heat treatments in 20/80 H2/N2 replaces cage trapped O2- ions forming C12A7:H− followed by UV irradiation to generate C12A7:e− with electrical conductivities of 35 mS cm-1. C12A7:e- appears to belong to a new class of transparent conducting oxides (TCOs) that may offer commercial potential on further optimization due to low materials and processing costs, environmental stability, and natural abundance when processed efficiently.

Resettable Heterogeneous Catalyst: (Re)Generation and (Re)Adsorption of Ni Nanoparticles for Repeated Synthesis of Carbon Nanotubes on Ni–Al–O Thin Films

Liquid-feed flame spray pyrolysis (LF-FSP) of selected metalloorganics provides [NiO]0.25[Al2O3]0.75 and [NiO]0.5[Al2O3]0.5 spinel nanopowders (NPs) without aggregation and with good stoichiometric control. Both compositions were processed to thin films as a first step in preparing Ni:Al2O3 nanocomposite films for catalytic synthesis of CNTs. NPs dispersed in polymer were cast giving 30 ± 10 μm green films that were debindered (370 °C), sintered at 1000–1500 °C/air, and then heated at 1000–1100 °C in H2/N2 5:95 to generate Ni particles as catalyst sites. These Ni particles promote the growth of CNTs. The CNTs were then oxidatively removed coincident with regeneration of the [NiO]1–x[Al2O3]x surfaces. Thereafter, reduction, CNT syntheses, and catalyst regeneration were repeated two times more. The quality and quantity of CNTs were the same after each cycle. This represents what we believe is a new, general approach to catalyst recycling/regeneration.

Flame Made Nanopowder Processing Results in Low Temperature Sintering of β'’-Al2O3 Thin Films (50 µm) with TiO2 and ZrO2 Addition

β’’-Al2O3 is used commercially as a Na+ conducting ceramic electrolyte for its high ionic conductivity (0.2-0.3 S cm-1 at 300°C) and low materials’ costs. However, for batteries using β'’-Al2O3, about half of the cell resistance arises from the electrolyte itself because traditionally processed electrolyte materials are 1-2 mm thick. One can anticipate dramatic drops in cell resistance at <100 µm. However, traditional high sintering temperatures of 1600 °C/0-4 h cause rapid and excessive Na2O loss driving formation of the β- rather than β'’-Al2O3 phase lowering ionic conductivities limiting final properties. Known methods of β'’-Al2O3 sintering commonly involve covering the sample with the same powder to reduce Na2O loss. The quality (phase, particle size, particle morphology, etc.) of the starting powder has been shown to have a strong effect on β’’-Al2O3 sintering behavior. In line with our latest success of using flame made nanopowders (NPs) to minimize the external energy input for sintering Li7La3Zr2O12, Li+ conducting ceramic electrolyte known for its difficulty in sintering, we show that the same can be achieved for β’’-Al2O3. In this study, β’’-Al2O3, TiO2 and ZrO2 NPs were produced by liquid-feed flame spray pyrolysis (LF-FSP). The NPs were then processed to green films (80 µm) by tape casting such that β'’-Al2O3 with 0, 1, 2, and 3 wt.% of TiO2 addition is produced. TiO2 was selected to aid sintering as Al3+ vacancies generated by Ti4+ doping promote the sintering process. Furthermore, low melting point (1050-1150 °C) Na2O-TiO­2 line compounds form inducing liquid phase sintering. As expected, superior densification of β'’-Al2O3 films occurs with increasing TiO2 wt. %. Near full densities are reached at ≥ 1360 °C/2 h with 2 and 3 wt. % added TiO2. However β’’-Al2O3 content reaches only ~65 wt.% and the orientation of the c-axis is perpendicular to the film surface per XRD. The preferred conduction plane is perpendicular to the c-axis reducing net conductivity. Also, the large grain sizes seen in the 2 and 3 wt. % TiO2 samples suggest liquid phase sintering. To perturb grain reorientation during liquid phase sintering, and also pin grain boundaries to reduce grain growth, we introduced 10 wt. % of ZrO2 with 2 and 3 wt.% TiO2. The added ZrO2 may also reduce Na2O loss rate by reducing surface exposure of β’’-Al2O3. Sintering of the aforementioned samples both reduces final grain sizes and degrees of c-axis orientation. Furthermore, nearly full densities could be accessed at 1320 °C/2 h with 85 wt.% β'’-Al2O3. Ionic conductivities obtained equal those reported by others. Our approach is scalable and economical for mass producing β'’-Al2O3 films. Furthermore, the combination of nanopowders with selected additives allows sintering β'’-Al2O3 at 1320 °C, the lowest ever reported. Work supported on NSF subcontract from Na4B to University of Michigan and by a give from Mercedes-Daimler.

Liquid-Feed Flame Spray Pyrolysis Derived Nanopowders As a Route to Electrically Conducting Calcium Aluminate (12CaO.7Al2O3) Thin Films

Transparent conductive oxides (TCOs) have extensive applications in the diverse optoelectronics applications. However, it is often difficult to identify transparent oxides with high electrical conductivity due to their intrinsically wide band gaps. Furthermore, those that have been identified as offering useful properties often contain high cost and/or toxic components (e.g. In2O3) or are difficult to process (e.g. CuAlO2) or both; leading to challenging commercialization issues. In comparison, CaO and Al2O3, traditional cement components, have long been studied and found to form multiple phases at different stoichiometric ratios. Among these, 12CaO.7Al2O3 (C12A7) in particular has received considerable recent attention because it is a novel type of TCO. C12A7 is a light metal oxide with a unique set of cage structures that can be processed to give transparent, dense films that are typically insulating but that can be easily transformed into a transparent semiconducting films. As formed, C12A7 consists of a set of cage structures wherein charge balance is maintained through incorporation of O2- ions in these cages. Hosono et al among other groups has discovered that these O2- ions can be replaced through H2 treatment with OH- and H- ions (C12A7:H). Most important is their finding that UV treatment of (C12A7:H) can be used to generate transparent electrides, (C12A7:e-) providing materials with conductivities as high as 1 S cm-1 in pellets or sputtered films. These materials thus offer the potential to process low cost TCOs at commercial scales providing simple processing routes to such materials can be developed. Traditionally, C12A7 materials have been processed using solid-state reactions followed by pulsed laser deposition (PLD) or floating zone (Fz) crystallization methods as high temperature, high cost approaches to single-phase films. These techniques require a significant number of process steps to generate C12A7:e. We demonstrate here an effective mass production method by producing C12A7 nanopowders (NPs) via liquid-feed flame spray pyrolysis (LF-FSP). Nearly fully dense, single phase, dense, flexible and transparent C12A7 thin films (< 30 m) can be produced by processing these NPs into green films by tape-casting, thermo-compression and then sintering to 1300/3 h/O2. Subsequent heat treatments in 20% H2/80% N2 to replace O2- ions forming C12A7:H- followed by UV irradiation provide C12A7:e- with electrical conductivities of 75 mS cm-1. C12A7:e- is expected to belong to a new class of TCOs due to its low materials and processing costs, environmental affinity, and natural abundance when processed efficiently.

Processing liquid-feed flame spray pyrolysis synthesized Mg0.5Ce0.2Zr1.8(PO4)3 nanopowders to free standing thin films and pellets as potential electrolytes in all-solid-state Mg batteries

Despite the intense concentration on lithium-based batteries, safety, ease of construction and cost continue to drive the search for alternatives that do not suffer from such restrictions. We present here preliminary work on the development of thin film Mg2+ conducting electrolytes as the key starting point for the development of all-solid-state Mg batteries. Initial studies explored compositions in the Mg0.5CexZr2-x(PO4)3 (x = 0.1, 0.2 and 0.3) system first as pellets and with somewhat optimized compositions (with x = 0.2) as thin films. Introduction of Ce allows sintering to full density at temperatures where Ce free films do not densify completely. The work reported here relies on the synthesis of nanopowders (NPs) using liquid-feed flame spray pyrolysis that offers the potential to reduce processing conditions, to control final average grain sizes (AGSs) and provide single-phase materials with good to excellent mechanical properties. The pellets and then thin (≤50 μm) films produced here show conductivities of up to 3 × 10−3 mS cm-1 at ≈ 300 °C, which if extrapolated (using an Ea of ≈30) to 400 °C would be close to 10−2 mS cm−1 in keeping with the best reported values in the literature. The thin films reported here offer nearly full densities beyond what is currently achievable by any other method. The ionic area specific resistance (IASR) values for these thin films were found to be 1400 Ω cm2 at 300 °C and are estimated to drop to 110 Ω cm2 at 400 °C, significantly lower than values for pellets reported elsewhere.

Evaluation of perovskite catalysts prepared by flame spray pyrolysis for three-way catalyst activity under simulated gasoline exhaust feeds

We have used liquid-feed Flame Spray Pyrolysis (FSP) to prepare a series of high surface area, nanocrystalline perovskites of general formula AA’BB’O3 (A = La, A’ = Ca, Sr, Y, Ce; B = B’ = Mn, Fe, Co, Ni). Use of the FSP method has allowed the systematic investigation of changing both A site dopant and B site cation while maintaining high surface areas. The resulting perovskites have been evaluated for their CO, HC and NO (three-way catalyst (TWC)) activity under simulated gasoline exhaust feeds, their oxygen storage properties and their stability to high temperature redox conditions. The activity of the perovskites has been compared to a low loaded commercial PdRh TWC and were found to be significantly poorer after mild calcination and very significantly deactivated after high temperature hydrothermal redox ageing.

Co-Al spinel-based nanoparticles synthesized by flame spray pyrolysis for glycerol conversion

The catalytic properties of Co-Al spinel nanoparticles prepared by liquid-feed flame spray pyrolysis (L-F FSP) were investigated in the glycerol conversion in gas phase in an atmosphere of hydrogen. Reduction at 1123 K of the as-synthesized spinel nanoparticles induced the formation a new phase containing metallic cobalt species. Although, the reducibility of cobalt oxides is greatly decreased due to interaction with aluminium species, this strong interaction may prevent the aggregation of Co particles under the harsh reduction conditions. X-ray photoelectron spectroscopy (XPS) of the reduced spinel nanoparticles at 1123 K revealed that the Co/Al atomic ratio has decreased to Co/Al = 0.11, which may indicate a redistribution of the aluminum and cobalt species at the surface of the sample submitted to the reduction in a flow of hydrogen at 1123 K. X-ray diffraction (XRD) and high resolution electron microscopy (HRTEM) also reinforced the formation of metallic cobalt species after reduction of cobalt from the spinel nanoparticles at 1123 K. The main products obtained from the conversion of glycerol in the gas phase were hydroxyacetone, pyruvaldehyde, lactic acid and lactide. FSP ensured uniform dispersion of the active metal on a support material.

Bottom‐up vs reactive sintering of Al2O3–YAG–YSZ composites via one or three‐phase nanoparticles (NPs). Bottom‐up processing wins this time

AbstractThe bottom‐up approach describes the synthesis of bulk materials from the finest possible length scales to obtain the best global properties. This approach was adapted to the synthesis of multi‐phase ceramic composites produced from metal oxides produced by liquid‐feed flame spray pyrolysis (LF‐FSP). The effect of length scale of mixing was tested through two processing schemes, mixed single metal‐oxide nanopowders (NPs) and nanocomposite NPs having the desired composition within single particles. For the Al2O3–Y2O3–ZrO2 ternary system, composites prepared from nanostructured nanoparticles sinter to finer grain sizes (&lt;410 nm) at equivalent densities of 95%TD than those prepared from mixed nanoparticle processing. These contrast with our previous studies in this area where mixed NP processing gave the best or equivalent results. The nanocomposite NPs produced in this study exhibit novel nanostructures with three phases contained within single particles &lt;26 nm average particle size (APS). This nanostructure may directly explain the enhanced sintering of the nanocomposite NPs and may provide an impetus for future synthesis of similarly structured NPs.